A new study by research firm GfK provides a rare glimpse into the inner workings at Netflix, suggesting for one that the company’s highly publicized original series “House of Cards” may be less popular with viewers than acquired shows such as “Mad Men,” WSJ reports. “House of Cards” accounted for less than 1% of shows viewed by regular Netflix users during a week in April, according to the study, while old episodes of hit dramas “Breaking Bad” and “Mad Men” each got 3% of total viewership. The study has several limitations and is a far cry from offering traditional ratings, but it gives TV executives some data to work with as they struggle to gauge how popular their shows are on Netflix–and how to charge the streaming service for their content.